It’s a big change to the way Twitter fundamentally works. Previously, when you uploaded a picture to Twitter it was public by default, which was why you couldn’t send them via direct message. Now if you want to send a photo privately, that only you and the recipient can see, you can do that from right within the app.

This will probably be spun as Twitter taking on Snapchat, but that doesn’t seem quite right. Twitter’s photo messages don’t expire like Snapchat’s do. In fact, they can be saved to a device. But it does seem like a play to get in on the increasingly hot messaging market. The ability to send photos — along with a far more prominent Messages button — lets Twitter insinuate itself into the messaging wars. It comes just before Instagram is expected to announce its own private messaging feature, and gives the company the ability to threaten popular services like WhatsApp and Kik–and even more to the point, SMS.

“I think of private messaging as an important component of this public real time conversational distributed platform that Twitter is — this global town square. And it turns out that in this town square, you want to be able to have an aside with someone,” Costolo said. “I think the direct messaging, private messaging function of Twitter is an absolutely vital piece of being that global town square and bolstering those four pillars of public, real time, conversational and distributed.”

Private messaging in lieu of SMS is already massive in Asia, and growing phenomenally in the United States. Carriers have lost tens of billions of dollars in SMS revenue in recent years, as services like WhatsApp, Kik, LINE, and WeChat have exploded, particularly among a very valuable youth market.

Given Twitter’s strategy of steady incremental change in recent years, this probably isn’t the end point of its play for messaging. But it certainly seems like a new beginning for one its oldest features.